The present application claims priority to Japanese Patent Application No. 11-80964 filed Mar. 25, 1999, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical waveguide, and specifically relates to a multi-layer optical waveguide constructed as a light source for a laser beam printer.
2. Description of the Related Art
There has been strong demand for increasing the speed of laser beam printers accompanying digitalization and the development of information networks in recent years. Increasing the speed of rotation of the polygonal mirror used for scanning has been proposed as one means of increasing the speed of the laser beam printer. It is difficult to increase the speed of rotation of the polygonal mirror beyond the current condition because the surface of the polygonal mirror may become distorted by the centripetal force when the number of rotations of the polygonal mirror approaches 50,000. Conventionally, the surface of a photosensitive body is scanned via a plurality of laser beams in order to increase the recording speed of laser beam printers.
Specific examples include Japanese Laid-Open Patent Application No. HEI 10-282441, and U.S. Pat. Nos. 4,637,679, 4,547,038, and 4,958,893 which disclose proposing or using constructions for regulating a plurality of laser beams at suitable spacing by optically deflecting a plurality of laser beams using a polarization beam splitter, half mirror, reflection of a prism surface and the like. However, these methods are disadvantageous in that alignment of the beams becomes difficult when there are many laser beams, the size of components increases, and cost becomes excessive. For these reasons, it is extremely difficult to increase the speed beyond current conditions.
Methods of construction using a plurality of laser light sources arranged at very small pitch, the so-called multi-light source method, is desirable. This method includes the so-called array laser method of forming laser diodes on a substrate as a multi-laser light source, the method of light emitted from optical fiber as a secondary light source, and a method using an optical waveguide to reduce the pitch on the exit side to be narrower than the entrance side, as disclosed in Japanese Laid-Open Patent No. SHO 54-7328.
When considering the state of image formation on the surface of a photosensitive body in methods using array lasers, the pitch of the arranged laser diodes is desirably at very small spacing of less than 100 xcexcm so as to have a plurality of laser beam spots in sufficient proximity. However, forming laser diodes on a substrate at such a fine pitch is difficult due to disadvantageous heat generation. For this reason, other methods using optical fiber or optical waveguides are deemed effective.
When a plurality of laser beams are used, the laser beam spots on the surface of the photosensitive body must mutually overlap so as to record without gaps on the surface of the photosensitive body. At this time, the required overlap on the surface of the photosensitive body may not be obtained even if, for example, an optical waveguide is used to narrow the pitch on the light exit side when does not overlap even though the core pitch of the light exit edge is reduced to the lowest limit.
The reason for this situation is that the beam spot diameter is thinned and reduced when the laser beam spot pitch on the photosensitive surface is also reduced using a reducing optical system. Although types which use optical fiber rather than optical waveguides have been considered, types using optical waveguides characteristically provide greater freedom from the perspective of narrowing a plurality of optical paths.
FIGS. 1(a)-1(c) schematically show the construction of a conventional light waveguide for narrowing the pitch on the light exit side, and the scan line produced thereby. FIG. 1(a) shows a plan view, FIG. 1(b) shows the light exit side at the right side of the plan view. FIG. 1(c) shows the state of the scan line recording on the photosensitive body surface. As shown in FIG. 1(a), a conventional optical waveguide is formed by a plurality of optical waveguides 2 on a substrate 1. The pitch Pb of the light exit end 2b of the waveguide 2 at the light exit side 1b of the substrate 1 is narrower and has a tighter structure than the pitch Pa of the light entrance end 2a of the waveguide 2 at the light entrance side 1a of the substrate 1. As shown in FIG. 1(b), the light exit end 2b of the waveguide 2 is arranged as a single core row on the light exit side 1b of the substrate 1.
When scanning in the main scan direction indicated by the arrow A using the aforesaid conventional optical waveguide, a plurality of connected scan lines L are obtained in the main scan direction, as shown in FIG. 1(c), but a gap S is generated between each scan line L in the subscan direction indicated by the arrow B. The state of the scan line shown in FIG. 1(c) is shown viewed from the photosensitive body surface side.
To counteract these disadvantages, there is known art which does not use optical waveguides and collimates laser beams emitted from each laser beam light source via individual micro lenses so as to overlap the laser beam spots, such as disclosed in U.S. Pat. No. 5,737,300. However, such micro lenses are difficult to manufacture and position, and disadvantageously increase costs.
An object of the present invention is to eliminate the previously described disadvantages.
Another object of the present invention is to provide an optical waveguide and manufacturing method capable of ideally overlapping laser beam spots on a photosensitive body surface.
These and other objects are attained by providing an optical waveguide, comprising a plurality of layers; and a plurality of cores provided in each of the at least two of the plurality of layers, and arranged with staggered exits.
These objects are further attained by a method for manufacturing the optical waveguide, comprising the steps of: forming a bottom surface clad layers on a top surface of a substrate; forming a bottom core on the bottom clad layers; forming an overclad to protect the bottom core and the top surface of the bottom clad layers; polishing the top surface of the overclad; and forming a top core on the polished overclad.
The present invention produces an ideally overlapped laser beam spots on the surface of a photosensitive body via a simple arrangement and simple optical system. Furthermore, the generation of gaps in the scan line is prevented by multiple light sources.
If a core is laminated after the top surface of the overclad is polished to flatness, defects and the like of the core on the overclad can be prevented.